Saturday, 15 September 2012

CNC drill - more testing

Another Thursday, another post-Midnight testing session at BuildBrighton - this time we're trying to handle play in our cnc drilling machine which is still causing some of our boards to be drilling slightly off.
We managed to get the drill head spinning the right way, and slow down the servo movement (rather than just ram the drill bit into the cutting board at full speed) and it's certainly helped.

Here's the latest test board fresh off the cnc:

We started in the top right hand corner. Around the centre of the board, the drill isn't quite 100% bang on, but is about as accurate as we usually get when drilling these things by hand, with a little Dremel and snake-head attachment, so it should be good enough.

The three holes at the bottom left of the board were totally way out with the printed PCB, but did actually marry up with the on-screen display

So either the PCB layout has changed between printing our test boards onto paper (not impossible) or the software is reading the dxf/nc drill file incorrectly and putting the holes for the transistor at the bottom-right corner in the wrong place!
It shouldn't take a massive amount of work to find out what went wrong and why, and maybe even tighten up some of the inaccuracies around some of the holes.

At the minute, our path-finding is still doing "nearest-non-drilled-hole"

Given that we start in the top-right hand corner, the y-axis travels "downwards" for a total of nine holes, while the x-axis moves left to hit hole 5 and then right onto hole 6 (the x-axis doesn't change in order to then drill holes 7,8 and 9). At hole 10 the y-axis moves in the opposite direction (upwards) and it's around the centre holes that there's a lot of backwards and forwards movements. It's also around these centre holes that we're seeing most inaccuracies.

The next plan is to alter the path-finding in the software so that it starts at the top of the board, and only ever travels in one direction on the y-axis. This should eliminate any backlash in at least one axis and hopefully give us a level of accuracy that we'd be happy to live with, and then we can get on with the exciting stuff like publishing it all online for everyone else to have a go with!

EDIT: Do'h. We were indeed using two different boards for testing! Here's a screenshot of the PCB layout used to load the holes into our CNC. Note how the transistor in the bottom right hand corner has moved down in relation to the rest of the board. If we had printed this board and drilled it, it's looking quite likely that we'd have had a successful test much earlier on!